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Herein, a novel sound energy acquisition device based on a flexible electrospun polyvinylidene fluoride (PVDF) nanofibrous membrane was developed. Effects of electrospinning and the addition of silver nanoparticles (AgNPs) on the crystal structure and piezoelectric properties of the PVDF nanofibrous membranes were examined. Electrospinning and the addition of AgNPs effectively induced the formation of the β-phase and increased the piezoelectricity. The piezoelectric electrospun PVDF samples were crucial for converting sound energy into electric potential and absorbing sound waves. Moreover, the use of piezoelectric shunt damping reduced the sound transmission at low frequencies. Therefore, the electric energy generated in the low-frequency region was higher than in mid- and high-frequency regions. The electric power of PVDF/AgNP was 7・10–4 W – a significant increase of 40% compared to PVDF without AgNPs (5・10–4 W) at low frequency. This demonstrates that PVDF/AgNP presents excellent piezoelectric properties and acoustic–electric conversion characteristics. Hence, the piezoelectric PVDF device fabricated herein can not only reduce sound transmission but also convert the sound energy into electric energy. This novel sound energy acquisition device is practical and efficient in various sensing and energy harvesting applications, and will aid in the operation of low-power consumer electronic devices and to maintain a green environment.
In this work, the intrinsic drawbacks of polyhydroxybutyrate (PHB) such as slow crystallization rate, secondary crystallization and brittle nature were improved by blending with bio-based fillers, i.e. nanofibrillated/microfibrillated cellulose (NFC/MFC). A novel chlorinated-solvent-free based system was developed to blend PHB and NFC/MFC that resulted in homogenous dispersion of fibers in the PHB matrix, without the need for surface modification of fibers. The developed nano/micro-composite materials were fabricated as masterbatch pellets and films. Additionally, the effect of different NFC/MFC fiber morphologies influencing the crystallization behaviour of PHB was investigated in detail by differential scanning calorimetry, polarized optical microscopy and Fourier transform infrared spectroscopy. Both non-isothermal and isothermal crystallization studies (modelled with Avrami’s kinetics) were performed on nanocomposites and variations in crystallization kinetics of PHB after addition of NFC/MFC were determined. Addition of NFC/MFC resulted in the drastic increase in the crystallization rate of PHB and hence they acted as nucleating agents. The fine and homogeneous morphology of NFC produced smaller PHB spherulites and restricted the growth of secondary crystals, hence resulted in more flexible films than PHB or PHB-MFC films, as determined by the mechanical testing of films. The more heterogeneous morphology of MFC altered the PHB crystallization mechanism most, as seen from the distorted shape of PHB spherulites along with the higher Avrami exponent, i.e. n ≥ 3.
Interactions between polylactide matrix and additives bearing –COOH and –OH groups were studied for compositions of polylactide (PLA) and functionalized cyclotetrasiloxanes (CX–R, R = OH, COOH, COOMe). Inherent conformational flexibility of cyclotetrasiloxane rings enabled evaluation of supramolecular phenomena between hydrogen bondingcapable functional groups and the polylactide backbone, as well as their role in polymer crystallization. The modification of PLA with CX–R was clearly reflected in the polymer dielectric response, unobscured by interfacial polarization effects frequently observed for other additives. New relaxation processes appeared next to the strong α-relaxation characteristic of the PLA matrix. Addition of CX–R influenced thermally induced crystallization of amorphous matrix as well as isothermal crystallization from melt. Development of crystals with 103 helical chain conformation was accelerated at relatively low temperatures in the presence of CX–OH with hydrogen bond donating hydroxyl groups. A specific phase separation that hindered mobility of polymer chains was observed in samples prepared with CX–COOH of strong hydrogen bond donor/acceptor ability. The presented results may be used as a reference for other systems with nanoadditives such as carbon nanotubes (CNT), graphene oxide (GO) or carbon quantum dots, in which interactions between –COOH/–OH groups and the polymer matrix play an important role.
Two-dimensional (2D) bilayer Janus pellicle (denoted as BJP) of concurrent double aeolotropic electrical conduction, superparamagnetism and luminescence is designed and constructed via electrospinning by using one-dimensional (1D) nanofibers and Janus nanoribbons as constructive units. The BJP comprises top-down two layers tightly bonded together. The top layer is a left-right structured Janus film which consists of Janus nanoribbons array as left and right side, and further, arrangement orientations of Janus nanoribbons in the two sides are perpendicular, leading to double aeolotropic conduction, and the conduction ratio reaches 108 times. The down layer is a non-array luminescent film made of nanofibers. Under the excitation by 291 and 294 nm light, red luminescence of the left side of the top layer and green luminescence of down layer in BJP are respectively achieved. The maximum saturation magnetization of the top layer can reach 21.45 (emu/g). By rolling the 2D BJP into the tube respectively with the ways of rolling from left to right or from up to down, three-dimensional (3D) dual-wall Janus-type tube with the Janus-type tube as outer or inner and the homogeneous tube as inner or outer is obtained.
The flower-like dendrimer and the nanosheet synthesis of polyaniline in the template-free method (rapid mixing) have been done successfully using p-aminoazobenzene (PAAB) and diazoaminobenzene (DAAB) as two new initiators, respectively. In both syntheses, the ammonium peroxydisulfate is used as an oxidant. The effect of initiators on the morphology is demonstrated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, and the mechanism of nanostructure formation is presented. The polymers are characterized by Fourier transform infrared (FT-IR) and Ultraviolet–visible (UV-vis) spectroscopies and elemental analysis (CHNS). Cyclic voltammetry (CV), electrical conductivity, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) are also presented. Both polymers are semi-crystalline in nature and had the same thermal behavior.
Calcium carbonate nanoparticles of calcite structure and nanometric size were successfully synthesized by mechanochemical processing using low energy mill (100 rpm). Transmission electron micrographs demonstrated that the nanoparticles tend to form agglomerates of approximately 1 µm due to their high surface energy. A study of structure and properties of composite materials resulting from the addition of CaCO3 nanoparticles at concentrations of 1, 2.5 and 5 wt% to epoxy resin was made. Epoxy/1 wt% CaCO3 and epoxy/2.5 wt% CaCO3 composites displayed an increase of 8 and 12°C in glass transition temperature (Tg), respectively. Scanning electron microscopy images of composites revealed a hierarchical structure of micrometric sized extended aggregates of nanometric calcium carbonate particles homogeneously distributed in the polymer matrix. This morphology explains the increase in hydrophobicity, as well as gains in Young’s moduli, which were greater than 59% with respect to the neat epoxy as measured by Nanoindentation. Therefore, this work demonstrates that the optimum range of concentration up to 2.5 wt% of high-quality nano CaCO3 guarantees thermal, mechanical and surface significant improvements associated with a hierarchical microstructure-nanostructure, which ultimately extend the possibilities of application of epoxy materials for nowadays challenges.
Shape memory polymers (SMPs) with novel functions have received increasing attention, but hyperbranched polyimide (HBPI)-based SMPs have rarely been reported. Herein, we have synthesized a series of thiol-ended hyperbranched polyimides (BTMP-n, n = 6, 9, 11) with various molecular weights using a thiol-ene click reaction, and BTMP-n was used as a crosslinking agent with 1-methacryl-allyl ethoxyethyl-diphenyl phosphate (AGDP) to prepare SMPs (BTMP-n-AGDP). The chemical structure and molecular weight of BTMP-n were characterized by Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, and matrix-assisted laser desorption ionization timeof-flight (MALDI-TOF) mass spectroscopy. The shape fixity ratios and shape recovery ratios of BTMP-n-AGDP were over 99% and over 90%, respectively, indicating excellent shape memory properties. The excellent cycling stability of BTMP-n-AGDP was also demonstrated using the shape recovery sharpness over consecutive cycles. A rapid transition between the temporary shape and permanent shape of the BTMP-n-AGDP was discovered using the large shape recovery sharpness and a cramped strain recovery transition breadth. The results provide a new method for obtaining high-performance SMPs.